Optical coupling

ABSTRACT

The present invention relates to an optical coupling between an end of an optical fiber and an end of a lens, which provides a reliable joint with a determined spacing and angular orientation. The optical coupling permits movement of the end of the optical fiber relative to the lens in at least two alignment directions. Advantageously, the present invention permits movement of the end of the optical fiber relative to the end of the lens in a direction perpendicular to the optical axis of the lens, before the optical coupling is secured. The optical fibre within an optical fiber tube/ferrule and the lens are secured within separate sleeves and the sleeves bonded together. The end of the optical fiber and the end of the lens are optically aligned before being secured in place relative to each other.

FIELD OF THE INVENTION

The present invention relates to an optical coupling system,particularly a connection system providing a reliable joint betweenoptical elements. In particular, the present invention provides anoptical coupling between an optical fibre and a lens.

BACKGROUND OF THE INVENTION

The most common optical connection used in manufacturing of opticaldevices is between an optical fibre end and a lens, such as a gradedindex (GRIN) lens. There are commonly two ways to make the connection.One common coupling system comprises a sleeve in which a fibre endwithin a supporting housing/ferrule is joined to a lens by attaching thesides of the ferrule and the lens to the interior bore of the sleeve.Manufacturing tolerances of, for instance, the lens diameter, theferrule diameter, or the dimension and position of the bore within theferrule, introduce variations which make it difficult to achieveaccurate alignment using this type of connection. The sleeve must have alarge enough internal dimension to accommodate a ferrule or lens at itslargest tolerance. As a result, smaller elements may unintentionallybecome misaligned with respect to other components within the sleeve.The fibre end within the ferrule is not always concentric. When theferrule internal diameter is too large for the fibre, the ferrule boreis not perfectly centred, or the fibre core is slightly off-centre, itbecomes necessary to adjust, or tune, the alignment of the fibre to thelens. This is difficult within the confines of the prior art couplingsleeve. Temperature changes in the environment also cause differentelements in the sleeve coupler to respond differently, further affectingthe quality of the coupling. In many instances, it is preferred to havethe fibre aligned at a port on the lens that is disposed adjacent to,rather than aligned with, the optical axis of the lens. This is notstraightforward within a sleeve connection.

Another common practice is to couple an optical fibre to a lens, such asa graded index (GRIN) lens, by placing the optical fibre into a ferruleor fibre housing and joining an end face of the ferrule directly to aface of the lens by applying a layer of adhesive between them. A directferrule to lens adhesive connection facilitates alignment of the coupledelements and provides a uniform joint. Planar end faces of the lens andferrule are reliably achieved to prevent unwanted tilt angle at thecoupling. Positioning the fibre adjacent to the optical axis of the lensis possible without the confining sleeve coupler. Also, relatively easyalignment tuning is possible to compensate for eccentric fibrepositioning within the ferrule. However, this method can only be usedfor lenses having flat surfaces which limits the applications of themethod. Further, spacing between fibre and lens has to be accuratelycontrolled which requires tight tolerance on the lens design.

To couple an optical fibre end to an optical element, such as a lens,several positioning variables exist: the spacing between the elementsand the coupling point relative to the optical axis are two of them.Common coupling techniques do not provide a convenient method ofadjusting the spacing between the elements and the coupling point at thesame time.

It is often desired to make a coupling with a precise predetermineddistance between elements, which is not practicable with a directadhesive connection. Fixing the elements with the desired separationbetween them is typically accomplished by securing them on a substratewith adhesive. However, it is difficult to establish an exact separationand alignment by this method.

The use of a single sleeve into which the ends of the optical fibre andlens are placed only allows adjustment during tuning/alignment along asingle axis, i.e., along the optical axis of the lens and thelongitudinal axis of the ferrule. It would be advantageous to be able toprovide additional directions for adjustment during tuning/alignment ofan optical coupling.

It is desired to provide a coupling system, which provides a reliablemeans for coupling between optical elements. It is also desired toprovide a coupling system, which can accurately control the spacingbetween optical elements, and provide adjustment to the alignment of thecoupled optical elements.

SUMMARY OF THE INVENTION

The present invention provides a spaced apart optical coupling foraccurately coupling between an optical fibre and a lens. The opticalcoupling comprising an end of the optical fibre and an end of the lenshoused respectively within separate sleeves. In addition, the presentinvention provides opportunity for tuning/alignment in more than onedirection before securing individual optical components and provides areliable uniform joint.

Accordingly, the present invention provides an optical couplingcomprising: an optical fibre housing having a longitudinal axis foraccommodating at least one optical fibre; a lens having an optical axis,the lens for directing a beam of light into the at least one opticalfibre and/or for receiving a beam of light from the at least one opticalfibre, a first sleeve for accommodating the optical fibre housing; asecond sleeve for accommodating the lens, the first and second sleevehaving complementary end faces that allow relative movement with respectto the optical axis of the lens and the longitudinal axis of the opticalfibre housing when inserted into their respective sleeves so that byadjusting the relative position of the two sleeves a preferred couplingis achieved. Preferably, the coupling is secured by forming an uniformjoint between the two complementary faces.

Accordingly, the present invention further provides an optical couplingcomprising: an optical fibre housing having a longitudinal axis foraccommodating at least one optical fibre; a lens having an optical axis,the lens for directing a beam of light into the at least one opticalfibre and/or for receiving a beam of light from the at least one opticalfibre, a sleeve for accommodating the lens, wherein at least a portionof the optical fibre housing and the sleeve have complementary end facesthat allow movement with respect to the optical axis of the lens and thelongitudinal axis of the optical fibre housing when the lens is insertedinto its sleeve so that by adjusting the relative position of the sleeveand the optical fibre housing a preferred coupling is achieved.Preferably, the coupling is secured by forming an uniform joint betweenthe two complementary faces.

The present invention extends to a method of coupling an optical fibreend supported in an optical fibre housing to a lens comprising the stepsof: disposing the optical fibre end supported in the optical fibrehousing within a first sleeve; disposing the lens within a secondsleeve, the first and second sleeve having complementary end facesabutting ends of the first sleeve and the second sleeve; aligningpositions of the optical fibre end and the lens relative to one another,whilst maintaining an epoxy free gap; securing the optical fibre housingand the lens into their sleeves and securing positions of the firstsleeve, the second sleeve by forming an uniform joint between the twocomplementary faces, such that they are immovable.

Advantages will be apparent to those skilled in the art with referenceto the detailed description of preferred embodiments and theaccompanying drawings, which illustrate preferred embodiments of theinvention by example only.

BRIEF DESCRIPTION OF FIGURES

An embodiment of the invention will now be described in conjunction withthe attached drawings in which like reference numerals designate likeitems:

FIG. 1 is a cross-sectional side view of a single optical fibre heldwithin an optical fibre housing in the form of an optical fibre tube.The single optical fibre and the optical fibre tube terminate in a flushslanted polished end face. A lens is also shown terminating in a slantedpolished end face.

FIG. 2 is a perspective side view of a lens and a plurality of opticalfibres held within an optical fibre tube. The plurality of opticalfibres and the optical fibre tube terminate in a flush slanted polishedend face and the lens terminates in a complimentary slanted polished endface.

FIG. 3 is a cross-sectional side view of prior arts single sleeveoptical coupling holding optical fibres within an optical fibre tube anda lens having slanted polished end face. In

FIG. 3(a) fibre tube and lens are secured to side walls of the sleeveand in FIG. 3(b) a space between the end faces of the optical fibres andthe lens is filled with adhesive.

FIG. 4 is a cross-sectional side view of the optical coupling of thepresent invention. A plurality of optical fibres are held within anoptical fibre tube. The plurality optical fibres and the optical fibretube terminate in a flush slanted polished end face. A lens is alsoshown terminating in a slanted polished end face. The polished slantedend faces are held within respective sleeves that are abutting andsecured in place by a uniform joint between end faces of the sleeves.

FIG. 5 is a cross-sectional side view of the optical coupling of thepresent invention substantially similar to that of FIG. 4 except thatinstead of the lens protruding from its sleeve, the plurality of opticalfibres held within the optical fibre tube protrude from its sleeve.

FIG. 6 is a cross-sectional side view of the optical coupling of thepresent invention substantially similar to that of FIG. 4 except thatrespective end faces of the plurality of optical fibres and the lens donot protrude outside their respective sleeves.

FIG. 7 is a cross-sectional side view of a single sleeve opticalcoupling of the present invention. A plurality of optical fibres areshown held within a single sleeve. A lens is shown within a sleeve. Theplurality of optical fibres and the single sleeve terminate in a flushslanted polished end face and the lens terminates in a slanted polishedend face. The slanted end faces are shown complementary one to another.

FIG. 8 is cross-sectional side view of another optical coupling of thepresent invention. A plurality of optical fibres are held within anoptical fibre tube. The plurality of optical fibres and the opticalfibre tube terminate in a slanted flush polished end face and the lensterminates in a slanted polished end face. The optical fibre tube has astep portion, which abuts against a complementary end of thecomplimentary sleeve.

FIG. 9 is an illustration of optical couplings of the present inventionproviding an input port to an optical device and an output port from theoptical device.

DETAILED DESCRIPTION OF FIGURES

An optical coupling is provided which preferably uses two sleeves withcomplimentary end faces to provide an optical coupling between anoptical fibre and a lens that are distant from one another. The couplingas described herein negates a need to have adhesive within the opticalpath and provides substantial flexibility for optical alignment of theoptical fibre and the lens and also provides a reliable and stablejoint.

Referring to FIG. 1, shown is a cross-sectional side view of knowncomponents to be optically coupled, namely an optical fibre 30 and alens 45. The lens 45 is for directing a beam of light into the opticalfibre and/or for receiving a beam of light from the optical fibre 30.The optical fibre 30 is held within an optical fibre tube/ferrule 25,which is supporting the optical fibre 30 and secured thereto. Theoptical fibre tube 25 has an end 6 and the optical fibre 30 has an end35. The ends are polished flush. The ends 35 and 50 are polished to thesame complementary non-perpendicular angles. For simplicity a singlefibre 30 is shown. In operation, when the optical fibre 30 and the lens45 are aligned, light propagates through the fibre and propagates fromthe end of the fibre as a point light source. Light propagating from theend 35 of the optical fibre 30 enters and is collimated by the lens 45.

Referring to FIG. 2, shown are a lens 45 and a plurality of opticalfibres 30 supported and held within a fibre tube 25, that are known. Theend 6 of the fibre tube 25 is shown in perspective having a plurality ofoptical fibre end faces 35. The end 50 of the lens 45 is shown inphantom. In operation, when the optical fibres 30 and the lens 45 arealigned, light propagates through the fibres and from the end face ofthe optical fibres 30 as point light sources. Light propagating from theend faces 35 of the optical fibres 30 enters and is collimated by thelens 45.

Referring to FIG. 3(a), shown is a prior art single sleeve coupling 8 inwhich a single sleeve 3 houses a fibre 30 supported and held within afibre tube 25 and optically coupled to a lens 45. As is evident fromFIG. 3(a) the single sleeve 3 allows little variation in geometricalconstraints before securing the fibre tube 25 and the lens 45 in place.Prior to securing it is possible to: a) rotationally align the fibretube and lens; and b) vary the distance between end faces 35 and 50 ofthe optical fibre 30 and the lens 45, respectively. However, in terms ofdesired geometric manipulations the two possible geometric manipulationsare not sufficient. It would be advantageous to be able to align theoptical fibre 30 and the lens 45 in a direction perpendicular to theoptical axis of the lens 45. The prior art single sleeve opticalcoupling 8 shown in FIG. 3 prevents manipulations to align the opticalfibre 30 and the lens 45 in a direction perpendicular to the opticalaxis of the lens 45.

FIG. 3(b) shows another prior art coupling method where the fibre tube25 and lens 45 are secured to each other by an epoxy 38. In this methodrelative position of the tube and lens can be adjusted in directionperpendicular to the optical axis of the lens 45, but the epoxythickness is difficult to control due to tolerances in lens dimensionswhich could cause unstability.

In contrast to the prior art coupling discussed above, the presentinvention allows the optical fibres 30 and the lens 45 to be aligned bymovement perpendicular to the optical axis of the lens while alsoproviding a uniform joint between the components. Heretofore, this hasbeen desirable. Referring to FIG. 4, shown is an optical coupling 10 ofthe present invention. A first sleeve 15 and a second sleeve 20 havecomplementary abutting ends indicated by line 17. Positioned within thefirst sleeve 15 is an optical fibre tube/ferrule 25 supporting andsecured to an optical fibre 30, the optical fibre 30 having an end face35. The end face 35 of the optical fibre 30 is flush with an end 40 ofthe optical fibre tube 25. The end face 35 of the optical fibre 30 andthe end 40 of the optical fibre tube 25 are polished such that they arenon-perpendicular to the longitudinal axis defined by the optical fibretube 25. That is to say, the end face 35 of the optical fibre isslanted. Positioned within the second sleeve 20 is a lens 45, forexample a GRIN lens. The lens 45 also has a slanted end face 50complementary to the slanted end face 35 of the optical fibre 30. Thetwo end faces 35 and 50 are secured relative to one another whilstmaintaining a gap between them. Instead of joining the two end faceswith an epoxy as practised in the art, the optical fibre tube 25 issecured to the first sleeve 15 and the lens 45 is secured to the secondsleeve 20, and the two sleeves are secured to each other. Ananti-reflective coating applied to the end faces of the elementsminimizes reflection resulting from refractive index changes of theresulting gap between optical elements

Referring again to FIG. 4, the optical coupling 10 is secured byapplying a surface securing means, for example an epoxy, to thecomplementary abutting end faces 17 and internal surfaces of thesleeves. The joint so formed is substantially uniform in nature. Thesurface securing means is not limited to adhesive. Adhesive for securingoptical components are understood to include: epoxy; metal solder; glasssolder; liquid glass; glue; etc. Alternatively, optical elements may beprovided, for instance, with a metal coating for soldering to sleeves.Of course, any method selected should result in a somewhat uniformjoint. A method of forming the optical coupling 10 is to first securethe lens 45 within the second sleeve 20 such that the end of the rodwith end face 50 lens protrudes from the second sleeve 20.Alternatively, the end face 50 does not protrude from the second sleeve20 and is instead inset a distance relative to the fibre tube 25 inorder to result in a desired gap. Position the first sleeve 15 in anabutting position against the second sleeve 20 as shown in FIG. 4 withthe optical fibre tube 25 in place. Alternatively the optical fibre tube25 is inserted after positioning the first sleeve 15 in the abuttingposition. Rotationally align the optical fibre 30 and the lens 45 suchthat the end faces 35 of the optical fibres 30 and the end face 50 ofthe lens 45 are complementary to each other. Tuning the optical couplingbetween the optical fibre 30 and the lens 45 is now possible in threedirections that are substantially orthogonal to each other. The firstdirection is provided by moving the optical fibre tube 25 in a directionalong the longitudinal axis of the optical fibre tube 25. In thismanner, the two end faces 35 and 50 are moved towards each other or awayfrom each other. The second and third directions are adjusted by slidingthe abutting ends 17 against one another such that the two end faces 35and 50 are moved relative to each other in directions perpendicular tothe longitudinal axis of the fibre tube 25. In this manner, tuning ofthe optical coupling is accomplished without obstructing or hinderingthe quality of the optical transmission. Of course, when a gap betweenthe optical elements is of a known distance, the optical fibre tube 25is fixed within the first sleeve 15 and tuning along its longitudinalaxis is not performed. Alternatively, when a gap of any small size isdesired between the optical elements, the optical fibre tube 25 is fixedwithin the first sleeve 15 and tuning along its longitudinal axis is notperformed.

The lens 45 as shown in FIG. 4 protrudes into the first sleeve andrestricts movement in the direction perpendicular to the longitudinalaxis of the fibre tube 25, i.e., horizontal axis. In this embodiment,the fibre tube 25 is of a larger diameter than the lens 45. As will beevident to one skilled in the art, it is possible to manufacturecomponents of differing sizes according to requirements. The order ofaligning optical components is not at the essence of the invention. Itis possible to align by initially sliding the abutting ends 17 againstone another and then moving at least one of the end faces 35 and 50along the longitudinal axis of the optical fibre tube 25. Alternatively,the process of alignment is an iterative sequential process. It iswithin the scope of the present invention for the lens 45 and the fibretube 25 to each be secured in a predetermined fashion within theirrespective sleeve and the end faces then aligned by movement of thesleeves orthogonal to the longitudinal axis of the fibre tube 25. As isnow apparent, the present invention provides advantages over the priorart single sleeve optical coupling 8 exemplified in FIG. 3. Anopportunity for tuning/alignment in more than one orthogonal directionis an advantage provided by the present invention.

Referring to FIG. 5, shown is an embodiment in which the optical fibretube 25 protrudes into the second sleeve 17. In this embodiment, thefibre tube 25 is of a smaller diameter than the lens 45. In a similarmanner to the optical coupling of FIG. 4, before securing the sleevestogether, a limited movement in the direction perpendicular to thelongitudinal axis of the fibre tube 25 is provided.

Referring to FIG. 6, shown is another embodiment. It is possibleaccording to the invention for the end face 35 of the optical fibre 30and the lens to be aligned without limiting movement in a directionperpendicular to the longitudinal axis of the fibre tube 25.

Alternatively, a single sleeve provides for an optical coupling 10.Referring to FIG. 7, a single sleeve 60 is used to optically couple thelens 45 to the optical fibre 30. The single sleeve 60 has an end 65slanted at substantially the same angle as the optical fibre tube 25.The lens 45 is of a smaller diameter than the optical fibre tube 25, andis positioned within the single sleeve 60. The single sleeve 60 and theoptical fibre tube 25 have complementary abutting ends indicated by line67. The end 40 of the optical fibre tube is secured to the end face 65of the single sleeve. When the optical fibre tube 25 and the singlesleeve 60 are rotationally aligned a linear coupling is provided. It isnow possible to tune the optical coupling between the optical fibre 30and the lens 45 in three fashions. Moving the lens 45 along the opticalaxis within the single sleeve 60 provides for a first direction oftuning. In this manner, the two end faces 35 and 50 are moved towardseach other or away from each other along the longitudinal axis of theoptical fibre tube 25, whilst maintaining an air gap between the two endfaces 35 and 50. One skilled on the art will understand that the term"air gap" extends to other gasses or mixtures thereof, for examplenitrogen, neon, etc. By sliding the abutting ends 67 against each otherthereby moving the two end faces 35 and 65 relative to each other in adirection perpendicular to the longitudinal axis of the fibre tube 25,tuning is also achieved. Therefore, in a similar manner to thatdescribed in FIG. 4, tuning of the optical coupling is accomplishedbefore securing the optical fibre 35 and the lens 45 relative to eachother. The end 40 of the optical fibre tube 25 and the end 65 of thesingle sleeve 60 are bonded together, as are the lens 45 and the singlesleeve 60. Of course, when an embodiment such as that of FIG. 7 is used,tuning of an angular orientation between the lens 45 and the fibre tube25 is supported. Rotation of the sleeve, because of its slanted endface, varies an angle between the optical axes of the opticalcomponents.

Referring to FIG. 8, shown is another embodiment of a single sleeve 62optical coupling 10. The single sleeve 62 has a flat end 67substantially perpendicular to the optical axis of a lens 45. A fibretube 26 has two sections of differing diameters. A first section 68 of asmaller diameter than the lens 45 and a second section 69 of a largerdiameter than the lens 45. The lens fits into the single sleeve 62 aswell as the first section 68. A step portion 64 defining a boundarybetween the first section 68 and the second section 69 abuts against theend 67 of the sleeve. The step portion 64 is flat and substantiallyperpendicular to the longitudinal axis of the fibre tube 26. Asillustrated, the first section 68 and the second section 69 areconcentric, however this is not essential. Before securing the opticalcoupling 10, the step portion 64 and the end 67 of the sleeve 62, whichare complementary and abutting, permit movement perpendicular to theoptical axis of the lens. The first section 68 is of small enoughdiameter to allow movement within the sleeve but also serves to providea stop by limiting movement perpendicular to the optical axis of thelens. The process of alignment of the optical coupling 10 is similar tothat described above.

Referring to FIG. 9, the optical couplings 10a and 10b of the presentinvention are shown providing an input port and an output port to adevice 100. The device 100 is not at the essence of the invention andis, for example, an isolator, circulator or a filter etc. In operation,a light signal is fed through an optical fibre 30a, which is directedinto a lens 45a by geometrical constraints imposed by the opticalcoupling 10a as detailed above. The lens routes the light signal intothe device 100. A light signal emerging from the device 100 emerges viaanother lens 45b, which is directed into an optical fibre 30b.

Though the above description refers to GRIN lenses, it is also possibleto use other lenses in accordance with the invention. For example, theuse of conventional lenses such as aspheric lens, spheric lens etc. Ahermetic sealed coupling is also achievable using the present inventionby forming an hermetic joint between the complementary end faces of thesleeves and between the fibre housing and the sleeve at one end and thelens and the sleeve at the other end. For example, a fibre is insertedinto a fibre tube and joined thereto hermetically using solder. Thefibre tube and the sleeve are also coupled using an hermetic solderseal. When the sleeves are coupled using an hermetic joint, a hermeticseal results at one end of the joint. This is sufficient for sealing asingle end of the device. When necessary, the other end of the couplingis also hermetically sealed.

Though the preceding disclosure refers to ajoint that is somewhatuniform and more preferably substantially uniform, the uniform nature ofthe joint is only one of many advantages of the present invention. Ofcourse it is preferred. A similar coupling absent a uniform jointbetween sleeves, though not preferred, is also useful and advantageous.

The preceding examples are for illustration only, and are not intendedto be limiting. Numerous other embodiments will be apparent to oneskilled the art, without departing from the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:
 1. An optical coupling comprisingan optical fibrehousing for accommodating at least one optical fibre; a lens fordirecting a beam of light into the at least one optical fibre and/or forreceiving a beam of light from the at least one optical fibre; a firstsleeve for accommodating the optical fibre housing; a second sleeve foraccommodating the lens, the first and second sleeve having complementaryend faces that when contacting one another allow relative lateralmovement with respect to the optical axis of the lens and thelongitudinal axis of the optical fibre housing when inserted into theirrespective sleeves so that by laterally adjusting the relative positionof the two sleeves a preferred coupling is achievable prior to thesleeves being affixed together, the end face of the lens nearest theoptical fibre housing and the end face of the optical fibre being spacedfrom one another while the complementary end faces are touching; and,two complementary end faces of the sleeves having adhesive therebetweenjoining the two end faces, wherein the first sleeve and the secondsleeve comprise mating portions, the mating portions permittingrestricted relative movement of the sleeves in the plane orthogonal totheir longitudinal axes.
 2. An optical coupling comprising:an opticalfibre housing for accommodating at least one optical fibre; a lens fordirecting a beam of light into the at least one optical fibre and/or forreceiving a beam of light from the at least one optical fibre, a sleevefor accommodating the lens, at least a portion of the optical fibrehousing and the sleeve having complementary ends allowing relativemovement with respect to the optical axis of the lens and thelongitudinal axis of the optical fibre housing when the lens is insertedinto its sleeve, the end face of the lens nearest the optical fibrehousing and the end face of the at least one optical fibre being spacedfrom one another while the complementary ends are touching; and, anadhesive disposed on and between the two complementary end faces forsecuring the end faces relative to each other wherein the sleeve and theoptical fibre housing comprise mating portions, the mating portionspermitting restricted relative movement of the sleeve and the opticalfibre housing in the plane orthogonal to their longitudinal axes.
 3. Anoptical coupling as defined in claim 2, wherein a portion of the opticalfibre housing protrudes into the sleeve.